This invention relates to a method for removing a binder from a green body which is a shaped article formed of a powder material, and more particularly to a method for removing, from a green body which is generally prepared by forming a pellet of a powder material such as ceramic powders or particles, cermet powders or particles, metal powders or particles or the like using a binder and subjecting the so-prepared pellet to injection molding, the binder contained in the green body.
Recently, attention has been paid to the injection molding of a powder material such as ceramic powders or particles or the like from the viewpoint of a new method for preparing a shaped article.
Conventionally, the removing of a binder from a green body by thermal decomposition or degradation is practiced according to a method for removing a binder under pressure generally called a pressure degreasing method in the art and typically disclosed in Japanese Pat. Publication No. 33282/1987 and U.S. Pat. No. 4,305,756 or an unsaturation degreasing method disclosed in, for example, Japanese Pat. Publication No. 48563/1986.
In the pressure degreasing method, a pressure in a pressure chamber in which a green body is placed is raised to a level above the vapor pressure of a binder incorporated in the green body at an ambient temperature, so that the binder may be vaporized, resulting in volatilizing from the green body. This leads to the removal of the binder from the green body.
The unsaturation degreasing method is so constructed that a green body having a binder contained therein is placed on a binder absorbent and then heated to a temperature within the range between the melting point of a minimum-melting-point component of the binder and the melting point of a maximum-melting-point component of the binder, resulting in removing the minimum-melting-point component of the binder from the green body. Subsequently, the green body is heated to a temperature within the range between the melting point of the maximum-melting-point component and the sintering temperature of a powder material constituting the green body to remove the maximum-melting point component of the binder, resulting in the full removal of the binder from the green body.
Unfortunately, the above-described conventional binder removal methods by thermal degradation each requires to heat the green body to an elevated temperature. Also, the heating must be carried out for a long period of time. For example, the removal of the binder from the green body requires to heat the green body or binder for a period of time as long as from about three days to one week. Thus, each of the conventional methods requires much time and expense, resulting in the cost of a final shaped product being highly increased.